Telephone system



July 15, 1941. 1 J L, MERRILL, JR 1 2,249,156

TELEPHONE SYSTEM Filed Jail. 11, 1940 MASTER 87:47 ION J. L.MERR/LL,JR

ATTORNEY Patented July 15, 1941 UNITED STATES TELEPHONE SYSTEM Josiah L. Merrill, Jr., Jackson Heights, N. Y., 215- signor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 11, 194:0, Serial No. 313,308'

9 Claims. (01. 179-42) This invention relates to telephone systems and particularly to intercommunicating and conference systems.

It is the object of this invention to provide an improved system of intercommunication between a plurality of stations having normal central office or private branch exchange facilities.

This object is attained in accordance with a feature of the invention by an organization of circuits and associated apparatus whereby a subscriber at a master station equipped with a loud-speaking receiver and distant talking transmitter may communicate with the subscribers at one or more secondary stations and whereby the subscribers may employ the standard telephone handset for use on intercommunicating calls as well as on calls originating at, or extended to. a central ofiice or private branch exchange. I

A particular feature of the invention resides in a novel circuit arrangement involving a bridge type transformer, or hybrid coil whereby the.

receiver and transmitter elements of the standard handsets located at the several stations of the system may be connected to separate speech channels extending from the two pairs of line windings of the hybrid coil. V p

Another feature of the invention contemplates the use of switching means at a master station which functions to transform the intercommunicating system into a conference system, whereby the handsetsof all the subscribers of the system may be associated with a single' cen-i tral office or private branch exchange line for the purpose of receiving messages of common interest to all the subscribers. r

A further feature of the invention resides in the useof switching means at the various stations of the system which function to open the induction coil of the telephone set when the associated handset is employed on the'intercommunicating line in order that the subscribers ringer, associated with the central ofiice or private These and other features of the invention will be readily understood from the following detailed description made with reference to the ac-' companying drawing, the single figure of which illustrates an intercommunicating and conference arrangement embodying the features of the. invention;

Before entering into a detailed description of the operation of the system disclosed, a brief reference will be made to the apparatus located at each of the stations. The system comprises 'a master station A and a plurality of secondary stations such as B and C. In the drawing the station C is intended to represent the last station of the system, it being understood that other stations are interposed between this station and station B. v

The equipment at each of the secondary stations B and C is identical and comprises a stand.-

, ard telephone set or and associatedsubstation circuit including the induction coil 2].

or 3| and condenser 22 or 32, a buzzer 23 or33,

a ringer Her 34, a key 25 or and a relay 26por 3B. The ringer 24 or 34 1s employed on calls their respective lines LB or L0. The buzzers 23 33 areutilized to receive call signals originating at the master station A. A regular central oificej or private branch call is answerediin the usual manner by removingthe handset from itscradle support which, as is well known, results inthe, connection of the subscribers set to the line LB or Lo, as the case may be. In response to a'buzzer signal, the subscriber at a secondary station,

" actuates the key 25 or 35 and. removes the handset The relays 26 and 36 are controlled from the master station and function to complete the con-1 nection of the secondary subscribers sets to intercommunicatingline. V The master station A is furnished" with th same equipment as the secondary stations except that no buzzer or relay is required, and 'is also provided; with loud-speaking and distant talking facilities andwith switching devices whereby the buzzers and relays at the secondary stations may" be controlled, and whereby the intercornmunicat ing' system'may be transformed into a conference system for the 'purposeof rendering it possible' for all the subscribers of the system tobe connected to an incoming conference line for the receipt of a message or communication which" is of common'interest to all.

The following description is directed to the use of the system for intercommunication purposes during which a subscriber at the master station A may selectively signal and communicate with the subscribers at one or more of the secondary stationsB, C, etc; For purposes of illustration.

it will be assumed that the subscriber atthe master station A desires to communicate with the subscriber at station B and accordingly actuates the key 9 to the signaling position, that is, upwardly. The buzzer 23, at station B-is therew talking position. Relay 26 operates and connects the intercommunicating line to the contacts of key 25 at station B.

Upon hearing the buzzer signal 23, the subscriber at station B actuates the key 25 and removes the handset from its support. The calling and called subscribers may now communicate with one another.

When the key 25 at station B is actuated and the handset 20 removed from its support, two independent circuits are established, one involving the transmitter element of the handset 20 and the other involving the handset receiver element. The transmitter circuit may be traced from common conductor 40, conductor 4|, front contact and inner upper armature of relay 26, contacts 42 of key 25, conductor 43, transmitter of handset 26, conductor 44, contacts 45 of key 25, lower armature and front contact of relay 26, conductor 46, conductor 41 which, with conductors 40, forms speec'h channel T which terminates in .the right-hand windings of repeating coil R to which the talking battery 48 is connected. The left-hand windings of repeating coil R are connected to the input terminals of one-way amplifier 49 whose output terminals are connected to the line terminals of the lower line windings 50 of the hybrid coil H.

The other circuit which is effected by the actuation of key 25 and the removal of handset 20 from its support may be traced from the common conductor 40, conductor 4|, front contact and inner upper armature of relay 26, contacts 42 of key 25, conductor 5|, receiver of handset 20, conductor 52, contacts 53 of key 25, outer upper armature and front contact of relay 26, conductor 54, conductor 55 which, with conductor 40, constitute the other speech channel S, which extends from the output terminals of one-way amplifier 56 whose input terminals are connected to the line terminals of the line windings 51 of the hybrid coil H.

The speech transmitting circuit at the master station extends from battery 58, microphone 59 to the input windings 66 of coil H by way of .the normal contacts 6| and 62 of the key 63. The speech receiving circuit at the master station A includes the loudspeaker '64 and one-Way amplifier 65 which are bridged across the junction of hybrid coil windings 50 and 5'! by way of the normal contacts 66 and 61 of key 63.

From the foregoing description it is apparent that speech currents generated by the microphone 59 at the master station A are impressed upon the input winding 66 of hybrid coil H and the corresponding induced currents in the line windings 51 are amplified at 56 and traverse the speech channel S to activate the receiver element of the handset 20 at station B. It is also evident that the speech currents set up at the transmitter of handset 20 at station B traverse the speech channel T and are impressed upon the righthand win-dings of repeating coil B, so that the corresponding induced currents in the left-hand windings of repeating coil R are amplified at 49 and impressed upon the line windings 50 of hybrid coil H, from whence they traverse the normal contacts 66 and 61 of key 63, are amplified at 65 and impressed on the loud-speaker 64. Twoway conversation may be thus carried on between stations A and B.

It is obvious that the subscriber at master station A may converse with the subscriber at any other secondary station or may communicate with the subscribers at all of the secondary stations simultaneously, if circumstances warrant it. It is only necessary that the key 8 (individual to station C) or a plurality of such keys be first operated .to the signaling position and then immediately operated to the talking position in the manner described in connection with the operation of key 9.

It will be noted that when the handset 26 is removed from its cradle, the contact 10 is closed by the cradle plunger, which contact serves to complete the connection of the induction coil. 2| to the line LB. Should this coil be included in the line LB while the subscriber at station B is conversing on the intercommunicating line, its impedance during a signal transmitting period on line LB would result in the signal emitted by ringer 24 being attenuated. In order to preclude the possibility of a signal transmitted over line LB being inaudible to the subscriber at station B while conversing on the intercommunicating line, the cont-act 1| is provided on the key 25 which efiectively opens the induction coil to the line when the key 25 is operated. The ringer 24 will therefore operate as usual on a ringing signal incoming on the line LB.

In the event that the subscriber at station A desires to call in the subscribers at some or all of the secondary stations for the purpose of hearing a message incoming over the central ofi'ice or private branch exchange line LM from a distant point, it is necessary for the keys 8, 9 etc, to be actuated .to the signaling position and then operated to the talking position. These key operations signal the desired secondary stations and associate them with the intercommunicating line as before. The subscriber at the master station then actuates keys l3 and 63 and removes the handset I 6 from its cradle support while the subscribers at the called secondary stations actuate their keys, such as 25 and 35, and remove their handsets from their respective supports.

The actuation of key 63 at the master station A disconnects the loud-speaker 64 and microphone 59 from the hybrid coil H and substitutes for the former the line LM, and for the latter the balancing network I6. It is believed unnecessary to describe in detail the results effected by the removal of the handsets I6, 20, 36, etc, from their respective cradle supports and by the actuation of the corresponding keys I3, 25, 35, etc., since these results have already been set forth in connection with the response of the subscriber at station B to an intercommunicating call originated at station A. Sufiice it to say that the transmitters of all stations A, B, C, etc., are connected in parallel across the speech channel T and all the corresponding receivers are connected in parallel across the speech channel S. Thus speech currents incoming over the line LM traverse the line windings 5'! of the hybrid coil H, are amplified at 5'6 and impressed on the speech channel S across which the handset receivers of all stations A, B, C, etc., are connected in parallel. Speech currents generated at any of the handset transmitters of the various stations are impressed on the speech channel T, are amplified at 49 from whence they traverse the line LM by way of contacts'86 and BI of key 63, or pass through the hybrid coil windings 50 and 51, are amplified at 56 and impressed upon the speech channel S to be received by the receivers of each of the stations connected to the system.

The gains of amplifiers 45, 56 and 65 of the system are adjusted so as to provide satisfactory transmission between microphone 59 and each receiver of the secondary stations; between each transmitter of the secondary stations and the loudspeaker 64; and between each transmitter and receiver of the various stations. In the case of transmission across the hybrid coil H between transmitter and receiver of the various stations, the gains of the amplifiers are adjusted so that the effect of the air path between the loudspeaker 54 and microphone 59 is not noticeable.

It is apparent that the subscribers at the various stations may initiate and receive central ofiice calls in the usual manner over lines LA, LB and Lo and as hereinbefore mentioned, calls incoming over these lines may be indicated by the operation of the ringers 85, 24 and 34 even though the subscribers at whose stations the ringers are located are communicating on the intercommunieating line.

What is claimed is:

1. In a telephone system, a master station, a plurality of secondary stations each equipped with a telephone handset, a hybrid coil at said master station, a pair of one-way speech channels extending from said coil to said secondary stations, and means for connecting the transmitter and receiver elements of the handsets to separate speech channels.

2. In a telephone system, a master station having a distant talking transmitter and a loudspeaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation and having two pairs of line windings, a speech channel connected to each pair of line windings, a secondary station having a telephone handset comprising a transmitter and a receiver, and means for connecting the handset transmitter across one of said speech channels and the handset receiver across the other of said speech channels.

3. In a telephone system, a master station having a distant talking transmitter and a loudspeaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation and having two pairs of line windings, an amplifier having its input terminals connected to the line terminals of one of said pairs of line windings, a speech channel extending from the output terminals of said amplifier, a second amplifier having its output terminals connected to the line terminals of the other of said pairs of line windings, a speech channel connected to the input side of said second amplifier, a secondary station having a telephone handset comprising a transmitter and a receiver, and means for connecting the handset receiver across the first of said speech channels and the handset transmitter across the second of said speech channels.

4. In a telephone system, a plurality of central office lines, a subscribers station for each of said lines and having a handset comprising a transmitter and a receiver, a master station, a pair of speech channels, means comprising a hybrid coil interconnecting the master station with said speech channels, means at each of said subscribers stations for connecting the handset thereof to its respective central office line, and other means for connecting the transmitter of the corresponding handset to one of said speech channels and the receiver thereof to another of said speech channels.

5. In a telephone conference system, a master station having a distant talking transmitter and a loud-speaking receiver, a hybrid coil interconnecting said transmitter and receiver in conjugate relation and having two pairs of line windings, a central ofiice line circuit, switching means at said station for disconnecting said distant talking transmitter and said loud-speaking receiver from said hybrid coil and connecting said line circuit thereto, a speech channel connected to each of said pairs of line windings, a telephone handset at said station, and means thereat for connecting the transmitter of said handset to one of said speech channels and the receiver of said handset to the other of said speech channels.

6. In a telephone system, a master station having a microphone and loud-speaker, a hybrid coil interconnecting said microphone and loudspeaker in conjugate relation and having two pairs of line windings, a speech channel connected to each pair of line windings, said speech channels constituting an intercommunicating line, a secondary station equipped with a telephone handset, means at said master station for signaling said secondary station, means controlled from said master station for preparing the handset at said secondary station for connection to. the intercommunicating line, and means at said secondary station efiective subsequent to the operation of said master station controlled means for connecting the transmitter of said handset across one of said speech channels and the receiver of said handset across the other of said speech channels.

'7. In a telephone system, a master station havmg a microphone and a loud-speaker, a hybrid coil interconnecting said microphone and loudspeaker in conjugate relation and having two pairs of line windings, a speech channel extending from each pair of line windings, a telephone handset at said station, a central ofiice line, a balancing network, means for disassociating said microphone andv loud-speaker from said hybrid coil and substituting therefor said network and said central ofiice line, respectively, and means for connecting the transmitter of said handset across one of said speech channels and the re- I cating line comprising two speech channels, a subscribers telephone circuit comprising an induction coil and a handset comprising a transmitter and a receiver, a central ofiice line, means for effectively connecting the induction coil to said central ofiice line when said handset is to be used on said central oifice line, and means for opening said induction coil and connecting the transmitter and receiver to separate of said speech channels when said handset is to be used on said intercommunicating line.

JOSIAH 1.. MERRILL, R. 

